Published patent application WO2007/141688A1 discloses several embodiments of a color conversion element which may be used in a light source. A subset of the embodiments of the cited patent application relates to a color wheel comprising different sections. One of the sections is transparent or reflective and does not convert the color of the light which is transmitted or reflected through the color wheel. One or more other sections of the color wheel each comprise a luminescent material which converts the color of the transmitted or reflected light to another color. The light originates from a light emitter which emits light of a single color. The luminescent material or materials are chosen such that the light which is emitted by the light source is perceived by humans as light having a specific color distribution that is different from the color of the light emitter of the light source. The color wheel rotates in a light beam emitted by the light source and as such different colors of light are emitted successively in time. Due to the high speed of succession of the different colors humans perceive the emitted light as a light having the specific color distribution.
The color wheel has a disk shape and is subdivided in sections. Each section has a corner at the center of the color wheel and covers a certain angular distance of the imaginary circle formed by the outer edge of the color wheel. Multiple sections are combined to form the color wheel. The color wheel may have a small hole in the center. As shown in the figures, the diameter of the light beam is relatively small compared to the radius of the color wheel and, thus, a significant part of the color wheel is not used when converting the color of the light.
Besides the well-known use of phosphors in a dye, the color wheel of the cited patent application may be made of crystalline inorganic luminescent materials which are sintered into a light transmitting ceramic body. A disclosed manufacturing method of the color wheel is that the sections have to be manufactured first and that they have to be glued together. With respect to the manufacturing of the ceramic material only the general process of sintering has been mentioned.
The sections of the color wheel are relatively large and as such it is relatively expensive to manufacture the sections. Further, the shape of the sections must be very accurate because the color wheel cannot have any gaps between the sections. Basically two manufacturing methods are possible, either the ceramic sections are cut out of a plate of the ceramic luminescent material or the sections are directly manufactured at their required shape. When cutting out of a plate, a relatively large part of the plate is not used and, thus, wasted. Further, cutting out the section of a plate is a step which costs a lot of time and must be performed with very accurate, and thus expensive, cutting tools. When the sections have to be manufactured directly at their required shape, for example, via sintering, the process has to be very accurate to manufacture sections that may be combined to one color wheel without gaps between the sections. It is relatively difficult to manufacture ceramic sections with such an accuracy and is thus relatively expensive.